Apparent symmetry rising induced by crystallization inhibition in ternary co-crystallization-driven self-assembly

The concept of apparent symmetry rising, opposite to symmetry breaking, was proposed to illustrate the unusual phenomenon that the symmetry of the apparent morphology of the multiply twinned particle is higher than that of its crystal structure. We developed a unique strategy of co-crystallization-driven self-assembly of amphiphilic block copolymers PEO-b-PS and the inorganic cluster silicotungstic acid to achieve apparent symmetry rising of nanoparticles under mild conditions. The triangular nanoplates triply twinned by orthogonal crystals (low symmetry) have an additional triple symmetry (high symmetry). The appropriate crystallization inhibition of short solvophilic segments of the block copolymers favors the oriented attachment of homogeneous domains of hybrid nanoribbons, and consequently forms kinetic-controlled triangular nanoplates with twin grain boundaries.


Measurements
Nuclear magnetic resonance (NMR): 1 H NMR experiments were carried out on a Bruker ARX400 spectrometer at 25°C.The chemical shifts (δ) in 1 H NMR were reported in ppm relative to tetramethylsilane (TMS) as internal standard (0.0 ppm) or proton resonance resulting from incomplete deuteration of NMR solvent CDCl3 (7.26 ppm).Coupling constants (J) are expressed in hertz.

Gel permeation chromatography (GPC):
The number-average molar masses (Mn), weightaverage molar masses (Mw), and polydispersity indices (Đ = Mw/Mn) of the resultant polymers were estimated on a GPC instrument equipped with a Waters 515 HPLC pump and a Waters 2410 refractive-index detector.Three Waters Styragel columns with 10 μm bead size were connected in tandem.Their effective molar masses ranges were 100-10000 for Styragel HT2, 500-30000 for Styragel HT3, and 5000-600000 for Styragel HT4, respectively.The pore sizes were 50, 100, and 1000 nm for Styragels HT2, HT3, and HT4, respectively.THF was used as the eluent at a flow rate of 1.0 mL/min at 35°C.The calibration curve was obtained against polystyrene standards.
Transmission electron microscope (TEM): TEM, EDS, and selected area electron diffraction (SAED) images were obtained using Thermo Fisher Scientific (FEI) Tecnai F20 and JEOL JEM-2100 transmission electron microscope operating at 200 kV.The images were taken with Gatan Oneview IS camera.TEM samples were prepared by adding 10 μl solution to the thin pure carbon film coated Cu grids of 300 mesh and blotting away the excess solution with dust-free paper.
Scanning electron microscope (SEM): SEM images were obtained on a Zeiss Merlin Compact field-emission scanning electron microscope operated at 10 KV.The samples were prepared by dipping a drop of solution onto hydrophilic cleaning silica wafers kept at 25°C and the solutions were absorbed by dust-free paper after 15 s.The wafers were stuck to the conductive adhesive.

Atomic force microscope (AFM):
AFM images were performed on a Bruker BioScope Resolve under ScanAsyst mode in the air.The ScanAsyst-Air probe was used and has one silicon tip on the nitride lever with a reflective Al back side.Scan rate 1 Hz, Peak Force Amplitude 150 nm, Peak Force Frequency 2 kHz.The AFM samples were prepared on silica wafers, the method of which is similar to the SEM ones.

Grazing-incidence wide-angle X-ray scattering (GIWAXS):
The GIWAXS image was performed on SAXS Lab Ganesha calibrated by LaB6 and silver behenate.Grazing-incident angle 0.15°, sample to detector 100 mm, measure time 600 s.The GIWAXS samples were prepared on silica wafers, the method of which is similar to the SEM ones.
1 M HCl (200 mL) was added and extracted with dichloromethane (DCM, 2 × 200 mL).The organic extracts were collected, washed with water (200 mL) and saturated NaCl solution (200 mL) respectively, then dried with anhydrous Na2SO4.The solvent was removed under reduced pressure and the residue was purified by column chromatography on silica with the eluent (petroleum ether (PE) /ethyl acetate (EA) = 4/1, V/V).The crude product was recrystallized in PE to obtain 2.0 g of yellow powder with a yield of 30%.

Synthesis of the block copolymer polyethylene oxide-b-polystyrene (PEO-b-PS)
A series of block copolymers with different block ratios were obtained via reversible additionfragmentation chain transfer (RAFT) polymerization in solution.A typical process was presented as follows: The macromolecular chain transfer agent PEO45-DMP (117 mg, 0.05 mmol), styrene (260.37 mg, 2.5 mmol), initiator AIBN (1.64 mg, 0.01 mmol), and dry toluene (0.7 mL) were added to a Schlenk flask and stirred until dissolved.The system was degassed by freeze-pump-thaw three times, and the RAFT polymerization was performed at 90°C for 24 h.The reaction was quenched in liquid nitrogen.The reaction mixture was diluted and precipitated in a large amount of n-hexane, and a yellow solid (170 mg, 45%) was obtained.The dispersity Đ was 1.08 by GPC of THF eluent.

Preparation of silicotungstic acid hexahydrate (STA)
A large amount of commercial reagent silicotungstic acid hydrate (H4SiW12O40 • nH2O) was dissolved in deionized water to saturation and stirred for 10 minutes.The mixture was filtrated followed by concentration via heating at 100°C until the solution volume to 10 mL.A large number of colorless crystals were obtained at room temperature.The crystals were filtrated and ground into powder in an agate mortar, then heated at 100°C until no vapor was generated and transferred to a vacuum oven for further drying.After the crystal water is sufficiently removed, a white solid powder whose chemical structure was determined by thermogravimetric analysis (TGA) to be H4SiW12O40•6H2O was obtained.
TGA spectrum of STA ramp 10°C/min to 800°C under air flowing at 100 mL/min.1400 1200 1000 800 600 400 Wavenumber (cm -1 ) A typical experimental procedure of kinetic-controlled CCDSA: A series of solutions of silicotungstic acid (3 mmol/L) were prepared with THF containing 1 vol.%H2O and cooled at 0°C.The polymer mixed solution of n(PEO45)/n(PEO45-b-PS16) ~ 1/1 at a total concentration of 2.50 mmol/L in THF/DCM ~3/1 (V/V) were prepared and cooled at 0°C.A mixture of 100 μL polymer solution was slowly added with 50 μL STA solution at 0°C, stand for 24 h in the refrigerator, and then the self-assembled solution containing the triangular nanoplates was obtained without further treatment.
Experimental procedure of thermodynamic-controlled CCDSA: After the triangular nanoplates were obtained through the above experimental procedures, the self-assembled solution containing the triangular nanoplates was sealed and heated to 80°C for 10 minutes, gradually cooled to room temperature and stand for 1~ 3 days.

Le Bail refinement
Jana 2006 1 was used for Le Bail fitting, and the process is as follows:

Pattern matching
Import data collected by powder X-ray diffraction (PXRD); Select "Various CW formats → PANalytical XRDML→Bragg-Brentanno method-Fixed Divergence Slit"; Enter cell parameters and select "Kalpha1/Kalpha2 doublet→X-rays Cu"."Edit Powder parameters": In "cell" page select refinement of a, b, and c; In "Profile" page select "Gaussian" as peak-shape function with a cutoff to 12*FWHM and activate refinement of "GW"; In "Corrections" page activate refinement of "shift" and select "Legendre polynomials" with 5 terms for background calculation.
"Run Refine": The refinement will stop if max (change/s.u.) < 0.05."Show powder profile": The peaks are systematically broader, indicating that Lorentzian broadening is to be combined with the Gaussian profiles.
"Edit Powder parameters": In "Profile" page select "Pseudo-Voigt" and activate refinement of "LY " "Run Refine" "Edit Powder parameters": In "Profile" page activate refinement of "LX" "Run Refine": The peaks have no asymmetry problem, so activation and refinement of parameters "X+" and "X-" are not required.

Space group determination
"Tolerances for crystal system recognition": Maximal deviation for cell lengths in 0. "Final step of the space group test": Select accept the space group transformed into the original cell.
Run Le Bail refinement without reflections absent due to the new symmetry.

Calculation of Hanson solubility parameters
The term Hanson solubility parameter (HSP) 2 is an important quantity for predicting solubility relations and is defined as follows: HSP is a three-dimensional vector  ( D ,  P ,  H ), which can be well characterized by just three parameters  D for dispersion (van der Waals),  P for polarity (related to dipole moment), and  H for hydrogen bonding.The equivalent HSP for mixed solvent is the weighted vector sum of each component: The compatibility between two materials can be represented as the relative energy density (RED), which is defined as: Where Ra is the distance of HSP for two materials and is calculated as: R0 is the radius of the solute with which the other material must be compatible.

a
-b-PSn by RAFT.The degrees of polymerization (DPs) of the blocks were determined by 1 H NMR. b Mn and Đ were obtained by GPC in THF.c Yield was calculated before purification by preparative GPC.
02 Å; Maximal deviation for cell angles in 0.2°."Select Laue symmetry": Select Orthorhombic mmm Laue symmetry."Select cell centering": Select C centering (because it has low Rp factors and high extinction)."Select space group": Select C2221 (because it has low Rp factors and high extinction).
Le Bail refinement results of STA/PEO.

Supplementary Table 3. SupplementaryTable 3 .
RED less than 1 indicates high affinity, while RED more than 1 indicates low affinities.RED equal or close to 1 indicates a critical state.The HSPs of THF, EtOH, DCM, H2O, and PS are looked up and listed in Supplementary Table3, the R0 of PS is 12.7, and the solubility of PS in mixed solvents can be calculated and displayed in Hanson solubility parameters of mixed solvents and the solubility of PS.
a The subscripts denote the volume equivalent of the solvents.